With some people, you really can only wonder what they are thinking their behaviour will gain them.
I’ve had one who apparently felt so hurt at me quoting a price reflecting the 24-hour rate clearly indicated in my gig - for a same-day delivery of his job - that he felt the need to leash out in a nasty albeit smart enough way to not really have much to report, so I just blocked him, in case he might decide to want to direct-order just to be even nastier, and took a moment to silently pity him. After all, it can’t really be a good thing for you to be like that, even if you’ve made it to top buyer
At least, we have the block option to avoid working with such people if they message first.
Did you ask support something concrete like “can you please cancel this order for me because (reason, in your case, curse words and being insulting) and this should obviously not affect my ratings”?
I’ve had good experience with that, was told they cancelled with the least possible effect on my account, and my ratings weren’t affected, neither did I notice a drop in business. So maybe it affected my gig ranking, I guess, but it didn’t seem to really matter.
Or did you already do the job? In that case, of course, don’t cancel, you should be paid for your work and time, and the buyer issued a warning or suspended, if that’s their usual way of doing business conversation.
Maybe ask for a team lead to review your case, before giving up over one such case (at least, I dearly hope you don’t get cursing and insulting customers regularly!).